Articles prepared from fast ultraviolet radiation curing silicone composition

ABSTRACT

Compositions which cure by UV radiation in less than one second are obtained by mixing an alkenyl containing polydiorganosiloxane, a mercapto functional crosslinker of the mercapto functional polyorganosiloxane or mercapto organic compounds, a photosensitizer, a viscosity stabilizer, and optionally a reinforcing agent. These compositions can be packaged in one container and can be used as the primary coating for optical fibers.

This is a divisional of copending application Ser. No. 07/151,748 filedon Apr. 18, 1988 now U.S. Pat. No. 4,946,874, which application is acontinuation-in-part of application Ser. No. 545,729, filed Oct. 26,1983, abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a silicone composition which rapidly cureswhen exposed to ultraviolet radiation (UV).

2. Description of the Prior Art

UV curable silicone compositions are known in the art. Siliconecompositions which can be cured by exposure to UV radiation include twotypes of curing reactions. One such reaction is a reaction of analkenyl-containing polyorgano-siloxane with an organosiloxane containingsilicon-bonded hydrogen atoms in the presence of a UV photoinitiator.Another such reaction is a reaction of an alkenyl-containingpolyorganosiloxane with a mercapto functional polyorgano-siloxane in thepresence of a UV photoinitiator.

One use of UV curable silicone compositions would be to coat opticalfibers. The optical fiber industry appears to desire coatings which canbe applied from one package, storage stable compositions which rapidlycure upon exposure to UV radiation to give a coating with apredetermined refractive index. Making such compositions is a challengebecause getting one property into an acceptable range frequently causesanother property to become unacceptable. An object of this invention isto provide a composition which meets the accepted and desired propertyprofile as stated above.

SUMMARY OF THE INVENTION

This invention relates to a composition comprising a material which isstorable in one package, is viscosity stable indicated by the failure ofthe 25° C. viscosity to double when heated at 100° C. for 24 hours,cures when exposed to ultraviolet radiation of 70 millijoules or lessper square centimeter in one second or less where the ultravioletradiation includes a wavelength of 365 nanometers and is obtained bymixing (A) alkenyl functional, linear triorganosiloxy endblockedpolydiorganosiloxane having a degree of polymerization of 30 to 1,000where each silicon-bonded organic radical is selected from vinyl,methyl, phenyl, 3,3,3-trifluoropropyl, beta-(cyclohexenyl)ethyl, ethyl,cyclohexenyl, allyl, higher alkenyl radicals represented by the formula--R*(CH₂)_(r) CH═CH₂ wherein R* is --(CH₂)_(s) -- or --(CH₂)_(t)CH═CH--, r has a value of 1, 2, or 3; s has a value of 3 or 6; and t hasa value of 3, 4, or 5, and silacyclopentenyl and having per molecule atleast two silicon-bonded organic radicals selected from vinyl,beta-(cyclohexenyl)ethyl, cyclohexenyl allyl, higher alkenyl radical andsilacyclopentenyl, (B) mercapto functional crosslinker which is at leastone material selected from mercapto functional polyorganosiloxanes andmercapto organic compounds, said mercapto functional polyorganosiloxanesare represented by the general formula

    R"R'.sub.2 SiO(R"'R'SiO).sub.x (R'RSiO).sub.y SiR.sub.2 'R"

wherein each R is selected from mercaptoalkyl radicals having from 2 to6 carbon atoms per radical: each R' is selected from methyl, phenyl,3,3,3-trifluoropropyl, and ethyl; and each R" is selected from theradicals of --OH, R, and R'; and each R"' is selected from methyl andphenyl, on the average there being per molecule at least twomercaptoalkyl radicals, x is 0 or greater, y is 0 or greater, and theamount and kind of organic radicals represented by R, R', R" , and R"'being of such a nature as to make (A) and (B) compatible, and saidmercapto organic compounds have at least two mercapto groups permolecule, consisting of atoms of sulfur, carbon, and hydrogen, andoptionally oxygen, having a molecular weight less than 1,000, and beingof such a nature as to make (A) and (B) compatible, (C) photosensitizer,(D) storage stabilizer, and (E) optionally reinforcing agent, therebeing in said material from 0.5 to 1.5 total alkenyl radicals permercapto group.

DETAILED DESCRIPTION OF THE INVENTION

The compositions of this invention have a definite property profilecovering both the uncured and cured states which permits them to beuseful in coating optical fibers particularly as the primary coat.

The compositions which are encompassed in this invention are thosedefined as one package compositions. For purposes of this invention,"one package compositions" means all of the ingredients can be combinedand then stored in a single package until cure is desired, at which timethe material can be removed from the storage container, exposed tocuring conditions, and it will cure to substantially the same propertystate after storage as it will prior to storage.

The compositions which are encompassed in this invention also do notdouble in 25° C. viscosity when heated at 100° C. for 24 hours,preferably they do not double in 25° C. viscosity when heated at 100° C.for seven days. The term "25° C. viscosity" means that the viscositybeing discussed is the viscosity as measured at 25° C. Such a propertyis important because in certain, in fact most, coating methods thecomposition will be exposed to high temperatures of hot optical fibersand because continuous coating methods are preferred and the mosteconomical. If the 25° C. viscosity were to vary widely after heatingwhich indicates that the composition is unstable, the coating thicknesscould vary by an unacceptable degree and in the most severe case thecomposition could gel.

The compositions which are encompassed in this invention can be cured byexposure to ultraviolet radiation which includes a wavelength of 365nanometers in one second or less and 70 millijoules or less per squarecentimeter. This limitation expresses the fast curing nature of thesecompositions. Compositions which require larger energies or longer timesto cure may find usefulness for certain applications but for purposes ofthis invention fast curing is necessary for todays manufacture ofoptical fibers. Compositions of this invention will cure in shortperiods of time using a medium pressure mercury vapor lamp. These curetimes are short such as less than 0.3 second, preferably 0.1 second orless, when exposed to UV radiation to provide 70 millijoules or less persquare centimeter of coating surface. Sources of UV provide a spectrumof wavelengths, but include the 365 nanometer wavelength for thisinvention. The UV source can be a mercury vapor lamp or other such knownUV sources.

The compositions which are preferred and encompassed by this inventionare those which are useful as primary coatings for optical fibers. Suchcompositions which exhibit a refractive index of less than 1.45 areuseful for reflective type coatings on optical fiber and those whichexhibit a refractive index of greater than 1.48 are useful fordispersive type coatings on optical fiber. The refractive index used isthat measured with sodium D line of 5893 Å at 25° C.

The compositions of this invention are made by mixing the followingingredients: (A) alkenyl functional linear triorganosiloxy endblockedpolydiorganosiloxane, (B) mercapto functional crosslinker (C)photosensitizer, (D) storage stabilizer, and (E) optionally reinforcingagent.

Polydiorganosiloxane, (A), is substantially linear. In the manufactureof such polymers some branching can occur. however, the amounts areusually very small and do not detract from the basic linear nature ofthe polymer chain. The silicon-bonded organic radicals can be vinyl,methyl, phenyl, 3,3,3trifluoropropyl, ethyl, beta-(cyclohexenyl)ethyl,cyclohexenyl, allyl, higher alkenyl radicals, and silacyclopentenyl, (A)should have at least two alkenyl radicals per molecule selected fromvinyl allyl, beta(cyclohexenyl)ethyl, cyclohexenyl, higher alkenyl, andsilacyclopentenyl. Because of availability and economicalconsiderations, the silicon-bonded organic radicals are preferablycombinations of vinyl, methyl, and phenyl. The degree of polymerizationfor (A) is from 30 to 1,000, preferably 50 to 500, repeating siloxaneunits per average molecule.

Polydiorganosiloxanes of (A) which contain higher alkenyl radicals haveat least two siloxane units of the following general formula ##STR1##wherein c is 1 or 2 and R** is an unsaturated radical. (A) can be acopolymer of the siloxane units and siloxane units having methyl,phenyl, ethyl, and 3,3,3-trifluoropropyl. Preferably, at least 50percent of the organic radicals are methyl.

The higher alkenyl radicals of R** can be selected from the groupconsisting of alkenyl radicals represented by the formula --R*(CH₂)_(r)CH═CH₂ wherein R* is --(CH₂)_(s) -- or --(CH₂)_(t) CH═CH--, r has thevalue of 1, 2, or 3; s has the value of 3 or 6; and t has the value of 34, or 5. While the odor emitted upon UV curing is significantlydecreased when at least 50 mole percent of the unsaturated radicals arehigher alkenyl radicals, it is even more preferred that essentially allthe unsaturated radicals be higher alkenyl radicals to further reduce oreliminate the emission of odor.

The higher alkenyl radicals represented by the formula --R*(CH₂)_(r)CH═CH₂ contain at least 6 carbon atoms. For example, when R* is--(CH₂)_(s) --, the higher alkenyl radicals include 5-hexenyl,6-heptenyl, 7-octenyl, 8-nonenyl, 9-decenyl, and 10-undecenyl. When R*is --(CH₂)_(t) CH═CH₂ --, the higher alkenyl radicals include, amongothers, 4,7-octadienyl, 5,8-nonadienyl, 5,9g-decadienyl,6,11-dodecadienyl and 4,8-nonadienyl. Alkenyl radicals selected from thegroup consisting of 5-hexenyl, 7-octenyl, 9-decenyl, and 5,9-decadienylare preferred because of the more ready availability of the α,ω-dienesused to prepare the alkenylsiloxanes. It is more preferred that R*denote --(CH₂)_(s) -- so that the radicals contain only terminalunsaturation and it is most preferred that R* is the 5-hexenyl radical.

When higher alkenyl radicals are present in the polydiorganosiloxane of(A), it is preferred that the units be selected from the groupconsisting of dimethylsiloxane units, trimethylsiloxane units,alkenylmethylsiloxane units, methylphenylsiloxane units,diphenylsiloxane units, and alkenyldimethylsiloxane units. Examples ofsiloxane units which form the polydiorganosiloxane (A) of this inventioninclude trimethylsiloxane units, dimethylsiloxane units,5-hexenyldimethylsiloxane units, 5-hexenylmethylsiloxane units,dimethylvinylsiloxane units, methylvinylsiloxane units,dimethyl-7-octenylsiloxane units, methyl-7-octenylsiloxane units,diphenylsiloxane units, methylphenylsiloxane units,9-decenyldimethylsiloxane units, 9-decenylmethylsiloxane units,5,9g-decadienyldimethylsiloxane units, 6-heptenylmethylsiloxane units,and dimethyl-8-nonenylsiloxane units.

Specific examples of (A) when the polydiorganosiloxane contains higheralkenyl radicals for purposes of illustration include ViMe₂ SiO(Me₂SiO)₁₀₀ (HexMeSiO0₂ SiMe₂ Vi, ViMe₂ SiO(Me₂ SiO)₂₀₀ (HexMeSiO)₁₀ SiMe₂Vi, HexMe₂ SiO(Me₂ SiO)₁₅₀ -(HexMeSiO)₄ SiMe₂ Hex, Me₃ SiO(Me₂ SiO)₁₀(HexMeSiO)₅ SiMe₃, HexMe₂ SiOSiMe₂ Hex, Me₃ SiO(HexMeSiO)₁₀ SiMe₃ andHexMe₂ SiO(Me₂ SiO)₁₅₀ SiMe₂ Hex where Me is the methyl radical, Hex isthe 5-hexenyl radical, and Vi is the vinyl radical.

The higher alkenyl radical containing polydiorganosiloxane of (A) thatare used in the coating composition of this invention can be prepared byseveral methods. For example, known siloxanes bearing reactive groupssuch as SiH may be reacted with an α,ω-diene such as 1,5-hexadiene.Alternatively, suitable olefinic organosiloxanes may be prepared fromalkenyl substituted silanes or siloxanes using well known methods ofhydrolysis and equilibration. It is usually preferred to prepareolefinic siloxanes by hydrolyzing a silane such as5-hexenylmethyldichlorosilane in excess water and then equilibrating theresulting hydrolyzate with cyclopolydimethylsiloxanes and a siloxaneoligomer containing alkenyldimethylsiloxane end groups using a basecatalyst such as KOH. However, it is believed that the olefinicpolydiorganosiloxanes of this invention may also be advantageouslyprepared in a one-step acid-catalyzed process wherein a silane such as5-hexenylmethyldichlorosilane is hydrolyzed and simultaneouslyequilibrated with cyclopolydimethylsiloxanes and1,3-dialkenyl-1,1,3,3-tetramethyldisiloxane.

For compositions which have a refractive index of less than 1.45 at 25°C., (A) is preferably a polydiorganosiloxane having a combination ofmethyl and vinyl radicals. Preferred (A) for the low refractive indexcompositions can be represented by the formula ##STR2## where m has anaverage value of from 80 to 500 and n has an average value of 0 to 10inclusive. The polymers of (A) where n is a larger number can be usedwith (B) which have two mercapto groups per molecule.

For compositions which have a refractive index greater than 1.48 at 25°C., (A) is preferably a polydiorganosiloxane having a combination ofvinyl, methyl, and phenyl radicals. The preferred (A) for this use haveat least 20 percent of the organic radicals being phenyl. The preferred(A) for high refractive index compositions can be represented by theformula ##STR3## where p has an average value of from 50 to 500, g hasan average value of from 0 to 10 inclusive, and the average value of rbeing such that the mol percent of (C₆ H₅)₂ SiO units is 20 to 30inclusive based on the total number of moles of siloxane units in thepolydiorganosiloxane. The polymers of (A) where q is a larger number canbe used with (B) which have two mercapto groups per molecule.

The mercapto functional crosslinker, (B), can be either a mercaptofunctional polyorganosiloxane, a mercapto organic compound, or mixturesthereof. The mercapto functional crosslinkers are selected such that thepolydiorganosiloxane, (A), and mercapto functional crosslinker, (B), forcompatible. The combination of (A) and (B) are compatible when specificpolymers or compounds are combined in the amounts to be used, and theresulting mixture does not separate into phases. A cloudy mixture canindicate separate phases and may separate on standing, such combinationsare not included within the scope of this invention. A cloudy mixturecan be within the scope of this invention if the storage, viscositystability, and cure properties are met. The selection for compatibilitycan readily be determined for any specific polymer or compound. Eachkind of unit in (A) and its amount will influence the compatability with(B) in which its kind and amount will influence the compatibility.

(B) should have at least two mercapto groups per molecule, preferablythe number of mercapto groups in (B) is three or more. The molecules of(B) which contain two mercapto groups are used with (A) in which n or qhave large values, such as 10. Preferably, (B) has three or moremercapto groups per molecule because present experimental work suggeststhat faster UV cures can be obtained with this type of composition.

The mercapto functional polyorganosiloxanes can be represented by thegeneral formula

    R"R.sub.2 'SiO(R"'R'SiO).sub.x (R'RSiO).sub.y SiR.sub.2 'R"(III)

where each R is mercaptoalkyl of 2 to 6 carbon atoms per radical, eachR' is methyl, phenyl, 3,3,3-trifluoropropyl, or ethyl; each R" is --OH,R, or R'; and each R"' is methyl or phenyl. There is on the average atleast two mercapto groups per molecule, x is 0 or greater, and y is 0 orgreater. Examples of mercapto functional polyorganosiloxanes whichcontain hydroxyl endgroups are hydroxyl endblockedpolymethyl(gamma-mercaptoisobutyl)siloxane hydroxyl enblockedpolymethyl(gamma-mercaptopropyl)siloxane where these polymers have from3 to 20 mercapto containing siloxane units.

For low refractive index, less than 1.45, compositions, preferred (B)can be represented by the average formula

    (CH.sub.3).sub.3 SiO({(CH.sub.3).sub.2 SiO}.sub.w {R(CH.sub.3)SiO}).sub.z Si(CH.sub.3).sub.3                                        (IV)

where R is gamma-mercaptopropyl or mercaptoisobutyl, w has an averagevalue of 3 to 12 and z has an average value of 2 to 8. For the highrefractive index, greater than 1.48, compositions, preferred (B) of thesiloxane type can be represented by the average formula

    (CH.sub.3).sub.3 SiO({(CH.sub.3).sub.2 SiO}.sub.a {R(CH.sub.3)SiO}).sub.b Si(CH.sub.3).sub.3                                        (V)

where a has an average value of from 0 to 1, b has an average value offrom 2 to 20, and R is gamma-mercaptopropyl or mercaptoisobutyl.

The mercapto functional crosslinker, (B), can also be a mecapto organiccompound, especially for compositions which have a refractive indexgreater than 1.48. These mercapto organic compounds are also known inthe art by terms such as "polythiols" and "polymercaptans". Thesemercapto organic compounds contain at least two mercapto groups (--SH)and consist of atoms selected from sulfur, hydrogen, and carbon, andoptionally oxygen. Preferably, these mercapto organic compounds containfrom 2 to 6 mercapto groups. Some examples are2,2'-dimercaptodiethylether,dipentaerythritolhexa(3)-mercaptopropionate), glycol dimercaptoacetate,glycol dimercaptopropionate, pentaerythritoltetra(3-mercaptopropionate),pentaerythritol tetrathioglycolate, polyethylene glycoldimercaptoacetate of the formula

    HSCH.sub.2 COOCH.sub.2 (CH.sub.2 OCH.sub.2).sub.11 CH.sub.2 OOCCH.sub.2 SH,

polyethylene glycol di(3-mercaptopropionate) of the formula

    HSCH.sub.2 CH.sub.2 COOCH.sub.2 (CH.sub.2 OCH.sub.2).sub.11 CH.sub.2 OOCCH.sub.2 CH.sub.2 SH,

trimethylolethane tri(3-mercaptopropionate), trimethylolethanetrithioglycolate, trimethylolpropane tri(3-mercaptopropionate), andtrimethylolpropane trithioglycolate.

The photosensitizer, (C), is a compound which will initiate a reactionbetween alkenyl radicals bonded to silicon atoms and mercaptoalkylgroups when irradiated with ultraviolet light. The photosensitizer iscompatible in the composition. Compatability of the photosensitizer canbe determined by mixing the ingredients and the photosensitizingcompound in an amount of one weight percent based on the weight of thecomposition and then mixing for up to 16 hours at room temperature,heating at 80° C. for up to four hours, or both. The photosensitizer issaid to be compatible if the composition is clear and thephotosensitizer has dispersed. Besides compatibility, thephotosensitizer should not cause the composition to react undesirably,such as gelling during storage. Some compounds which can be used asphotosensitizer in this inventive composition are: benzophenone,acetonaphthone, acetophenone, benzoin methylether, benzoin isobutyether,2,2-diethoxyacetophenone, ##STR4## These photosensitiziers representsome compounds which function to an acceptable degree in this invention.The most preferred photosensitizers are 2,2-diethoxyacetophenone and##STR5## Polysilanes are also useful as photoinitiators in thecompositions of this invention. The polysilane photoinitiators which areuseful are those which are compatible in the compositions. Thepolysilanes can be the phenylmethylpolysilanes defined by West in U.S.Pat. No. 4,260,780, issued Apr. 7, 1981 which is hereby incorporated byreference; the aminated methylpolysilanes defined by Baney et al. inU.S. Pat. No. 4,314,956, issued Feb. 9, 1982, which is herebyincorporated by reference; the methylpolysilanes of Peterson et al. inU.S. Pat. No. 4,276,424, issued Jun. 30, 1981 which is herebyincorporated by reference; and the polysilastyrene defined by West etal. in U.S. Pat. No. 4,324,901, issued Apr. 13, 1982 which is herebyincorporated by reference.

The viscosity stabilizer, (D), is a material which is added to thecomposition to assist in delaying or preventing the gellation of thecomposition during storage and at temperatures as high as 100° C. Thisviscosity stabilizer is compatible in the composition and keeps thecomposition from doubling in 25° C. viscosity when it is heated at 100°C. for 24 hours. Preferably, the composition does not double in 25° C.viscosity when heated at 100° C. for seven days. Amines are observed toserve as viscosity stabilizers. Presently, the most preferred amine forthis invention is 2-(diisopropylamino)ethanol. Another amine which issuitable, is trioctylamine. Another type viscosity stabilizer is a freeradical scavenger, such as p-methoxyphenol (also known asmonomethylester of hydroquinone, MEHQ), catechol, 4-t-butylcatechol,phenothiazine, hydroquinone, 2,6-di-t-butyl-p-methylphenol, andN-phenyl-2-naphthylamine. The free radical scavenger viscositystabilizers are used in amounts of preferably of zero to one weightpercent based on the weight of the composition, more preferably from0.01 to 0.1 weight percent. The most preferred free radical scavengerviscosity stabilizer is MEHQ.

The compositions of this invention can contain reinforcing agent, (E).The compositions preferably contain a reinforcing agent when a strongeror tougher cured product is desired or needed in the use. Preferably, areinforcing agent is present in the composition for optical fibercoating applications. If the composition of this invention is used forother than optical fiber coating, such as for coating electricalequipment and devices, it can contain many kinds of fillers asreinforcing agents such as fumed silica which can be untreated ortreated to make it hydrophobic such as with organosilanes,organosiloxanes, or organosilazanes. For optical fiber coatingapplications, the reinforcing agent should be a material which does notsubstantially increase the opacity of the composition compared to thecomposition without the reinforcing agent. For optical fiber coatingmaterials, the reinforcing agent is preferably present in an amount ofat least five weight percent. The reinforcing agent for optical fibercoating should also be non-abrasive to a glass surface, especially aglass surface of fiber to be used as an optical fiber. The optical glassfiber can contain certain claddings on its surface. The reinforcingagent is preferably a benzene soluble silicone resin when thecomposition is used as a coating for optical fibers. One preferredbenzene soluble silicone resin, as (E), contains trimethylsiloxy units,dimethylvinylsiloxy units, and SiO₂ units. The ratio of moles of

    (CH.sub.3).sub.3 SiO.sub.0.5 +(CH.sub.2 ═CH)(CH.sub.3).sub.2 SiO.sub.0.5 :SiO.sub.2

is from 0.5:1 to 1.1:1 and contains 1.7 to 2.0 weight percent vinylradical based on the weight of the resin. Other examples of siloxaneresins which can be used for reinforcing the composition of thisinvention when used as a coating for optical communications fibers are aresin having 5 mol percent dimethylvinylsiloxy units, 35 mol percenttrimethylsiloxy units, and 60 mol percent SiO2 units; a resin having 10percent dimethylvinylsiloxy units, 20 mol percent trimethylsiloxy units,and 70 mol percent monophenylsilsesquioxane units; and resins having 6.3to 15 mol percent dimethylvinylsiloxy units, 6.8 to 23.7 mol percenttrimethylsiloxy units, 0 to 45 mol percent monomethylsilsesquioxaneunits, and 35 to 85 mol percent monophenylsilsesquioxane units; resinswhich are copolymers of monopropylsilsesquioxane units andmonophenylsilsesquioxane units endblocked with dimethylvinylsiloxyunits; and a resin of trimethylsiloxy units and SiO₂ units endblockedwith diphenylvinylsiloxy units. For the high refractive indexcomposition based on polydiorganosiloxane having phenyl radical, thepreferred siloxane resins are the phenyl-containing siloxane resinsbecause these provide compatible compositions.

In addition to resins, the present compositions can be reinforced byusing mixtures of polydiorganosiloxanes for (A) in which at least onepolydiorganosiloxane has a low alkenyl radical content, such as is analkenyl endblocked polydiorganosiloxane and at least onepolydiorganosiloxane has a high alkenyl content such as 15 to 30 molepercent siloxane units containing alkenyl radicals. The amount of thehigh alkenyl content polydiorganosiloxane can be up to 25 percent of theweight of (A). The highest tensile strengths are obtained in the rangeof from 5 to 20 percent of high alkenyl content polydiorganosiloxane.For example, a mixture of polydiorganosiloxanes can be adimethylvinylsiloxy endblocked polydimethylsiloxane having a degree ofpolymerization of 50 to 300 mixed with a dimethylvinylsiloxy endblockedpolydiorganosiloxane having 78 mole percent dimethylsiloxane units and22 mole percent methylvinylsiloxane units and having a degree ofpolymerization of from 50 to 300 wherein the 22 mole percentmethylvinylsiloxane containing polymer is present in amounts of from 5to 20 weight percent.

Methods of mixing the ingredients (A) through (E) can be varied as longas the resulting composition cures when exposed to the UV energy asdefined. The mixing method should also not alter the one packagestability and the viscosity stability. Preferably, (A) and (B) aremixed, and then (C) and (D) are added and mixed using conventionalmixing equipment. When (E) is present, the preferred mixing procedure isto mix (A) and (E) and thereafter add the remaining ingredients. When(E) is the benzene soluble silicone resin as defined above, the mixtureof (A) and (E) may require heating or heating at reduced pressure toremove solvent in which the benzene soluble silicone resin is kept. Amixture of (A) and the benzene soluble silicone resin in xylene can beheated to about 100° C. at about 667 Pa to remove the xylene and form ahomogeneous mixture of (A) and the resin. Sometimes a mixture of (A),(B), and (C) and optionally (E), prepared at room temperature, areslightly cloudy, but become clear indicating compatibility when (D) isadded. Sometimes, if a mixture of (A), (B), and (C) and optionally (E),prepared at room temperature, do not become clear upon the addition of(D), heating the composition may product clarity (compatibility) whichwill remain after the composition has cooled to room temperature.

Although compatibility and clarity are preferred, such features shouldnot limit the use of the compositions of this invention in optical fibercoating applications, such as primary coatings and secondary coatingsbecause some types of optical fiber coatings do not need to be clear tofunction properly. An important limitation of the compositions of thisinvention is the ability to cure rapidly as indicated by the UVradiation energy requirement. The UV cure at 70 millijoules or less persquare centimeter coating surface should cure the composition in onesecond or less, preferably in less than 0.3 seconds. If the compositionis slightly cloudy and cures in these times with the stated UVradiation, then it is covered by the present invention. The compositioncan be prepared and stored in most equipment but some metals may causepremature reaction or cures, such as certain ferrous metals. Also, lightshould be avoided both during processing and especially during storage.

The compositions of this invention are mixtures of ingredients (A)through (E) which have a ratio of alkenyl radicals per mercapto group of0.5 to 1.5, thus the amounts of (A) and (B) are defined once thespecific polymers are stated. The amounts of (A) and (B) can vary if (E)is a vinyl containing benzene soluble silicone resin. Also, thecompositions preferably have a viscosity at 25° C. in the range of 1 to20 Pa's, most preferred is 1 to 8 Pa's.

Other ingredients which might be considered as useful in the presentcomposition are those which do not deleteriously alter the one packagestability, the viscosity stability, and the curing conditions. Suchingredients may be dyes, pigments, or other fillers. Some ingredients,such as certain fillers would not find utility as a prime coat foroptical fibers because such fillers would be abrasive, however, otherless sensitive applications may find such materials completely adequate.Another ingredient which might be added is a processing aid which helpsimprove the compatibility, viscosity or coating properties but otherwisedoes not substantially change the composition properties.

Preferred embodiments within the scope of the present invention arecompositions which have a low refractive index, as measured by thesodium D line at 25° C., n_(D) ²⁵ of less than 1.45, preferably about1.42 and compositions which have a high refractive index, as measured bythe sodium D line at 25° C., of greater than 1.48, preferably from 1.48to 1.55.

The low refractive index compositions are preferably obtained by mixing(A) a polydiorganosiloxane represented by formula (I), (B) a mercaptofunctional polyorganosiloxane of formula (IV), and (C)2,2'-diethoxyacetophenone or ##STR6## in an amount of 1 to 4 weightpercent based on the total weight of the composition, and the ratio ofvinyl radical per mercapto group is 0.57:1 to 1:1.25. These preferredcompositions can also contain an amine which does not increase theopacity of the composition compared to the composition without theamine, preferably the amine is trioctylamine or2-(diisopropylamino)ethanol which is present in an amount of from 0.5 to1.5 weight percent based on the total weight of the composition. Themost preferred low refractive index compositions are those which containthe benzene soluble silicone resin as defined above in amounts of 23 to37.5 percent by weight based on the total weight of the compositionbecause they are tougher and stronger. Those compositions which aredescribed as preferred low refractive index compositions preferably donot contain any other ingredients which alter the refractive index suchas increasing it to greater than 1.45. Most preferred low refractiveindex compositions have a refractive index of about 1.42.

The high refractive index composition, as preferred embodiments. can beof two types as identified by the type of crosslinker used, one usingmercapto functional polyorgano-siloxane and a second using a mercaptoorganic compound.

The preferred high refractive index compositions using the mercaptofunctional polyorganosiloxane crosslinker are those which are obtainedby mixing (A) a polydiorganosiloxane represented by formula (II), (B) amercapto functional polyorganosiloxane of formula (V), and (C)2,2-diethoxyacetophenone or ##STR7## in an amount of 1 to 4 weightpercent based on the total weight of the composition and the ratio ofthe vinyl radicals to mercapto groups is 0.57:1 to 1:1.25. Thesepreferred compositions can also contain an amine which does not increasethe opacity of the composition compared to the composition without theamine. Instead of an amine stabilizer these preferred compositions cancontain paramethoxyphenol as a stabilizer. The preferred high refractiveindex composition are those which have a refractive index as measured bythe sodium D line at 25° C. of greater than 1.48 especially those of1.48 to 1.55.

The other type of preferred high refractive index compositions are thosewhich are obtained by mixing (A) a dimethylvinylsiloxy endblockedpolydiorganosiloxane containing siloxane units selected fromdimethylsiloxane units, methylphenylsiloxane units, and diphenylsiloxaneunits where at least 30 percent of the organic radicals are phenyl. (B)a mercapto organic compound selected from at least one of

    CH.sub.3 C(CH.sub.2 OOCCH.sub.2 SH).sub.3,

    {(HSCH.sub.2 CH.sub.2 COOCH.sub.2).sub.3 CCH.sub.2 }.sub.2 O,

    C(CH.sub.2 OOCCH.sub.2 CH.sub.2 SH).sub.4,

    C(CH.sub.2 OOCCH.sub.2 SH.sub.4,

    CH.sub.3 C(CH.sub.2 CCH.sub.2 CH.sub.2 SH).sub.3,

    CH.sub.3 CH.sub.2 C(CH.sub.2 OOCCH.sub.2 CH.sub.2 SH).sub.3, and

    CH.sub.3 CH.sub.2 C(CH.sub.2 OOCCH.sub.2 SH).sub.3

and (C) 2,2-diethoxyacetophenone or ##STR8## in an amount of 1 to 4weight percent based on the weight of the total composition. Also thestabilizers can be present as stated above.

The compositions of this invention have numerous advantages over manyother compositions used for coating optical fiber as stated herein suchas it is one package storable, and has a viscosity which does not doublewhen heated at 100° C. for 24 hours. One advantage is the optical fibercan be made with low attenuation using this composition. Thesecompositions cure at room temperature by exposure to UV radiation. TheUV cure is so rapid that very high speed coating lines can be used, suchas 300 feet per minute. Cure times of 0.1 second are obtainable. Thecompositions of this invention are not severely inhibited by oxygen.

The compositions of this invention cure to elastomers which have arelatively low modulus, are tough, remain elastomeric over a broadtemperature range, such as from 80° C. to minus 60° C. for the lowrefractive index compositions. The compositions of this invention cureby an addition type reaction and do not give off by products.

Other utility of the compositions of this invention are wood finishing,textile coating, paper and plastic varnishes, adhesives, printing inks,metal decorating coatings, wire coatings, electronic encapsulants, andresist coatings.

The following examples are presented for illustrative purposes and arenot intended to limit the claims which are properly delineated in theclaims. All parts are parts by weight and viscosities are measured at25° C. unless otherwise stated.

EXAMPLE 1

A composition which cures to an elastomer by UV radiation was made bymixing 79.4 parts of a mixture of 32 weight percent xylene and 68 weightpercent of benzene soluble silicone resin (Resin I) containingdimethylvinylsiloxy units, trimethysiloxy units, and SiO₂ units wherethe ratio of the sum of the mols of dimethylvinylsiloxy units andtrimethylsiloxy units to SiO₂ units was 0.65:1 and there was 1.9 weightpercent vinyl radical in the resin with 100 parts of dimethylvinylsiloxyendblocked polydimethylsiloxane having a viscosity of about 2 Pa's(Polymer I). The resulting mixture was stripped of xylene by heating to100° C. at a pressure of about 670 Pa resulting in a clear polymer-resinblend (Blend I). A mercapto functional polyorganosiloxane of the averageformula ##STR9## (Crosslinker I) in an amount of 17.81 parts was mixedinto 80.23 parts of Blend I and then 0.98 part of photosensitizer,##STR10## and 0.98 part of 2-(diisopropylamino)ethanol was mixed to makea composition of this invention. The resulting composition was clear,had a viscosity of 2.08 Pa's. and was stored in a container opaque tolight including UV radiation. This composition remains unchanged inviscosity and cured properties after storage for over nine months.

The composition was coated on a monel wire of 125 microns to a thicknessof between 25 and 115 micrometers and then exposed to UV radiationgenerated by four medium pressure mercury vapor lamps equidistant fromthe wire and each other and also parallel to the wire. The compositionwas defined as cured when the surface was tack free and the physicalproperties were near maximum. The coated wire cured in less than 0.1second. The coated wire speed was 200 meters per minute through the UVlamp configuration. A sample of the composition was evenly spread on analuminum test panel in a thickness of about 200 micrometers, and thenexposed to UV radiation of 24 millijoules or less per square centimeterusing as a UV source a medium pressure mercury vapor lamp. The samplecured in 0.5 second. The cured sample was removed from the aluminum testpanel and cut into test pieces of 6.35 mm wide and about 3 cm long witha thickness of 125 to 150 micrometers. These test pieces were placed inan Instron tensile tester using a crosshead separation of 2 cm and thenthe elongation at break, the tensile strength at break, and modulus weremeasured. Six test pieces gave the average values of 3.17 MPa tensilestrength at break. 160% elongation at break, and a 50% modulus of 0.34MPa.

The cured composition had a refractive index. n_(D) ²⁵, of 1.416 and aTg of -126° C. The cured elastomer had a 2.5% modulus as follows

    ______________________________________                                        Temperature, °C.                                                                      2.5% Modulus, MPa                                              ______________________________________                                         80            0.017                                                           20            0.022                                                          -20            0.026                                                          -60            0.059                                                          ______________________________________                                    

Another composition was prepared as described above, the initialproperties were very similar to the initial properties of the firstprepared composition as indicated in Table I. The composition was heatedat 100° C. for the times indicated and then the viscosity at 25° C. wasmeasured, a sample was then cured and the tensile strength at break andthe elongation at break were measured as described above. The UV curetime after each aging time was 0.3 second or less at 24 millijoule persquare centimeter.

                  TABLE I                                                         ______________________________________                                        Aging Time,                                                                              Viscosity,  Tensile, Elongation,                                   Hours      Pa · s                                                                           MPa      %                                             ______________________________________                                         0         1.92        3.14     150                                            4         2.24        4.00     165                                           16         2.32        4.96     175                                           72         2.64        2.59     150                                           168        2.92        2.78     150                                           ______________________________________                                    

This example illustrates a low refractive index composition suitable foruse as the prime coating on an optical fiber made by melt drawing aglass fiber, and while still hot, such as about 200° C., into thecomposition and then exposing the coated fiber to UV radiation. Thisexample also illustrates the one package storage capability, theviscosity stability at 100° C. and the rapid UV cure times.

The composition was stored in a container opaque to UV radiation for 4hours and for two months and was then cured by exposure to UV radiationas stated above for making test pieces. The cure times were 0.5 secondand 0.6 second respectively. The cured physical properties were obtainedas described above and are reported in Table II.

                  TABLE II                                                        ______________________________________                                        Storage  Tensile,   Elongation,                                                                             50% Modulus,                                    Time     MPa        %         MPa                                             ______________________________________                                        4 hours  3.69       185       0.30                                            2 months 3.59       185       0.31                                            ______________________________________                                    

This data illustrates the storage stability in a one package container.A composition was prepared as described above except the2-(diisopropylamino)ethanol was left out. This composition gelled in afew days indicating that the viscosity stabilizer is necessary in thistype of composition for long storage periods.

EXAMPLE 2

A composition which cures to a high refractive index silicone elastomerwas prepared by mixing 89.03 parts of a polydiorganosiloxane of theaverage formula

    CH.sub.2 ═CH(CH.sub.3).sub.2 SiO{(CH.sub.3).sub.2 SiO}.sub.77 --{(C.sub.6 H.sub.5).sub.2 SiO}.sub.21 Si(CH.sub.3).sub.2 CH═CH.sub.2,

7.12 parts of a mercapto functional polyorganosiloxane (Crosslinker II)of the average formula ##STR11## and 3.85 part of ##STR12## Theresulting mixture was transparent and was packaged in a container opaqueto UV radiation. This mixture had a viscosity of 1.7 Pa's. andrefractive index, n_(D) ²⁵ of 1.488. Exposure to UV radiation from amedium pressure mercury vapor lamp in air which provided 24 millijoulesper square centimeter of composition surface of about 200 micrometersthickness cured the composition in less than 0.3 second. The curedelastomer had a tensile strength at break of 0.31 MPa. an elongation atbreak of 215%, and a 2.5% modulus of 0.007 MPa at 25° C. Thiscomposition is useful as a prime coat for optical fibers where arefractive index of greater than 1.48 is preferred or required. Thiscomposition illustrates the capability of fast cure by UV radiation.

EXAMPLE 3

A composition which can be cured by UV radiation to an elastomer wasprepared by mixing 94.22 parts of a dimethylvinylsiloxy endblockedpolymethylphenylsiloxane having an average of 48 methylphenylsiloxaneunits per molecule, 3.82 parts of

    CH.sub.3 CH.sub.2 C(CH.sub.2 OOCCH.sub.2 CH.sub.2 SH).sub.3

and 1.96 parts of ##STR13## The resulting mixture was transparent, had aviscosity of 11.3 Pa's, and a refractive index, n_(D) ²⁵ of 1.550. Acomposition in a thickness of about 200 micrometers cured in less than0.3 second to an elastomer having a tensile strength at break of 0.34MPa, an elongation at break of 120%, and a 2.5% modulus of 0.007 MPa at25° C. and a 2.5% modulus of 0.79 MPa at -60° C. This compositionillustrates the use of mercapto organic compound as the crosslinker fora siloxane polymer composition, a fast UV curing high refractive indexcomposition, and a composition useful as the primary coating for opticalfibers.

EXAMPLE 4

Several compositions were prepared by mixing a polydiorganosiloxane andResin I as described in Example 1 and then removing the xylene to make ablend of polymer and resin. The following ingredients were used to makecompositions as defined by Table III.

Blend II--47.2 parts of Resin I solids and 52.8 parts of adimethylvinylsiloxy endblocked polydimethylsiloxane having a viscosityof about 0.4 Pa's (Polymer II)

Blend III--50 parts of Resin I solids and 50 parts of Polymer I

Crosslinker III--trimethylsiloxy endblocked polyorganosiloxane having anaverage of 30 dimethylsiloxane units and 5 units ofmethyl(mercaptoisobutyl)siloxane

Crosslinker IV--trimethylsiloxy endblocked polyorganosiloxane having anaverage of 90 dimethylsiloxane units and 8 units ofmethyl(mercaptoisobutyl)siloxane

Crosslinker V--trimethylsiloxy endblocked polyorganosiloxane having anaverage of 18 dimethylsiloxane units and 3 units ofmethyl(mercaptoisobutyl)siloxane

Crosslinker VI--trimethylsiloxy endblocked polyorganosiloxane having anaverage of 24 dimethylsiloxane units and 4 units ofmethyl(mercaptoisobutyl)siloxane

Crosslinker VII--trimethylsiloxy endblocked polyorganosiloxane having anaverage of 61 dimethylsiloxane units and 7 units ofmethyl(mercaptoisobutyl)siloxane

Crosslinker VIII--trimethylsiloxy endblocked polyorganosiloxane havingan average of 41 dimethylsiloxane units and 7 units ofmethyl(mercaptoisobutyl)siloxane

Crosslinker IX--trimethylsiloxy endblocked polyorganosiloxane having anaverage of 45 dimethylsiloxane units and 3 units ofmethyl(mercaptoisobutyl)siloxane

Crosslinker X--trimethylsiloxy endblocked polyorganosiloxane having anaverage of 93 dimethylsiloxane units and 5 units ofmethyl(mercaptoisobutyl)siloxane

Crosslinker XI--trimethylsiloxy endblocked polyorganosiloxane having anaverage of 86 dimethylsiloxane units and 12 units ofmethyl(mercaptoisobutyl)siloxane

Crosslinker XII--trimethylsiloxy endblocked polyorganosiloxane having anaverage of 20 dimethylsiloxane units and 5 units ofmethyl(mercaptoisobutyl)siloxane

The compositions shown in Table III were prepared to have a ratio ofvinyl radical to mercapto group of 1.25:1 and each contained 0.29 partof 2,2'-diethoxyacetophenone and 0.29 part of trioctylamine. Thecompositions were made by blending the ingredients and the propertieswere measured as described in Example 1. The results for each of thecompositions are shown in Table IV. These compositions illustrate thevariety of mercapto functional polyorganosiloxane crosslinkers whichhave fast cure and can be used for a primary coat on optical fibers. Thecure time shown in Table IV was for UV radiation of a film thickness ofabout 200 micrometers.

                  TABLE III                                                       ______________________________________                                               Blend   Polymer    Crosslinker                                                                             Viscosity                                 Composition                                                                            No.    Parts  No.  Parts No.  Parts                                                                              Pa · s                   ______________________________________                                        A        II     19.08  II   5.35  III  4.57 0.96                              B        II     19.08  II   4.74  VIII 4.74 1.12                              C        II     19.08  II   2.50  IV   7.42 1.16                              D        II     19.08  II   5.05  V    4.87 0.92                              E        II     19.08  II   5.03  VI   4.89 0.92                              F        II     19.08  II   3.37  VII  6.55 1.08                              G        III    18     I    6.76  V    4.24 2.20                              H        III    18     I    6.74  VI   4.26 2.20                              I        III    18     I    5.21  VII  5.79 2.32                              J        III    18     I    7.02  III  3.972                                                                              2.32                              K        III    18     I    2.52  IX   8.482                                                                              1.64                              L        III    18     I    6.871 VIII 4.129                                                                              2.72                              M        III    18     I    1.233 X    9.669                                                                              1.96                              N        III    18     I    6.305 XI   4.695                                                                              2.80                              O        III    18     I    4.393 IV   6.607                                                                              2.32                              P        III    18     I    7.647 XII  3.353                                                                              2.64                              Q        III    18     I    8.494 II   2.506                                                                              2.76                              ______________________________________                                    

                  TABLE IV                                                        ______________________________________                                                          Cure    Tensile                                                                              Elonga-                                                                              50%                                            Compat-  Time,   Strength                                                                             tion   Modulus                               Composition                                                                            ibility  sec.    MPa    %      MPa                                   ______________________________________                                        A        Clear    0.4     1.44   124    0.37                                  B        Cloudy   0.4     1.20    92    0.46                                  C        Clear    0.4     0.90    90    0.41                                  D        Clear    0.4     1.14   115    0.32                                  E        Clear    0.4     1.26   111    0.34                                  F        Clear    0.4     0.88    78    0.46                                  G        Clear    0.4     1.26   128    0.27                                  H        Clear    0.4     2.76   166    0.30                                  I        Clear    0.4     1.41   111    0.40                                  J        Clear    0.32    3.53   188    0.34                                  K        Clear    0.63    1.12   128    0.27                                  L        Cloudy   0.32    1.17    93    0.37                                  M        Clear    0.32    0.90   119    0.29                                  N        Cloudy   0.32    2.03   138    0.38                                  O        Clear    0.32    1.88   150    0.34                                  P        Cloudy   0.32    2.20   172    0.38                                  R        Cloudy   0.32    2.00   202    0.22                                  ______________________________________                                    

EXAMPLE 5

A base was prepared by mixing 100 parts of a blend of 78.9 parts ofdimethylvinylsiloxy endblocked polydimethylsiloxane having a viscosityof about 40 Pa's and 21.1 parts of Resin I solids with 60 parts of fivemicron crushed quartz. A composition was prepared by mixing 16 parts ofthe base, 1.27 parts of Crosslinker I, 0.17 part of ##STR14## and 0.17part of 2-(diisopropylamino)ethanol. This composition had a ratio ofvinyl radical to mercapto group of 0.8:1. This composition in a filmthickness of about 200 micrometers cured by UV radiation with one passunder two medium pressure mercury vapor lamps at a rate of 10 m perminute. The resulting cured elastomer had a tensile strength at break of3.22 MPa, an elongation at break of 189%, and a 50% modulus of 0.66 MPa.This composition illustrates the fast cure nature in the presence of anextending filler.

EXAMPLE 6

Compositions which cure to an elastomer by UV radiation and which usepolydiorganosiloxanes containing higher alkenyl radicals were made bymixing the following ingredients:

Composition I

(a) 100 parts of a polydiorganosiloxane of the average formula ##STR15##

(b) 163 parts of a mercapto functional crosslinker of theaverage formula##STR16## and

(c) 8 parts of a photosensitizer of the following formula ##STR17##

Composition II

(a) 100 parts of a polydiorganosiloxane of the average formula ##STR18##

(b) 8 parts of Crosslinker XIII, and

(c) 3 parts of the photosensitizer described in (c) of Composition I.

Composition III

(a) 250 parts of a polydiorganosiloxane of the average formula ##STR19##

(b) 408 parts of Crosslinker XIII, and

(c) 20 parts of the photosensitizer described in (c) of Composition I.

Compositions I and III were clear and Composition II was cloudy. Each ofthe above compositions were cured by exposing them to UV radiation togive them 50 millijoules per square centimeter. Composition I cured to atack free elastomer having an elongation of about 25 percent.Composition II cured to a snappy elastomer with a very light tack on thesurface. Composition III cured to a tack free material with a lowelongation.

EXAMPLE 7

Compositions which cured to elastomer when exposed to UV radiation andwhich contained polydiorganosiloxanes having a high refractive indexwere made by blending a polydiorganosiloxane which was endblocked withdimethylvinylsiloxy units and contained about 66 mole percentdimethylsiloxane units and 34 mole percent diphenylsiloxane units andhad a degree of polymerization of about 100 and a mercapto functionalcrosslinker of the formula ##STR20## in amounts such that the ratio ofthe vinyl radical to mercapto group as shown in Table V. Thephotoinitiator (photosensitizer) in an amount of 2 weight percent andthe amine stabilizer and its amounts which were added to the blend ofthe polydiorganosiloxane and mercapto functional crosslinker aredescribed in Table V. The compositions were exposed to UV radiation for0.3 seconds (24 millijoules per square centimeter) and 0.7 seconds (50millijoules per square centimeter). The results of the exposure aredescribed in Table V in which "ST" means slightly tacky, "VT" means verytacky, and "T" means tacky. The appearance of the uncured composition asobserved is also described in Table V.

                                      TABLE V                                     __________________________________________________________________________    RATIO OF                                                                             PHOTO- AMINE TYPE                                                                            APPEARANCE                                                                             UV EXPOSURE                                    VINYL/SH                                                                             INITIATOR                                                                            (AMOUNT)                                                                              UNCURED  0.3 SEC                                                                            0.7 SEC                                   __________________________________________________________________________    0.67/1.00                                                                            1      DIPAE(0.25%)                                                                          Clear    ST   ST                                        0.80/1.00                                                                            1      DIPAE(0.25%)                                                                          Clear    ST   ST                                        1.00/1.00                                                                            1      DIPAE(0.25%)                                                                          Clear    VT   ST                                        1.25/1.00                                                                            1      DIPAE(0.25%)                                                                          Clear    VT   ST                                        0.80/1.00                                                                            1      None    Clear    ST   ST                                        0.80/1.00                                                                            1      DIPAE(0.25%)                                                                          Clear    ST   ST                                        0.80/1.00                                                                            1      DIPAE(1.00%)                                                                          Clear    T    T                                         0.80/1.00                                                                            1      TOA(0.25%)                                                                            Hazy     T    T                                         0.80/1.00                                                                            1      TOA(1.00%)                                                                            Clear    T    T                                         0.80/1.00                                                                            1      None    Clear    ST   ST                                        0.80/1.00                                                                            2      None    Clear    T    T                                         __________________________________________________________________________     Photoinitiator 1 was the compound described in Example 6, Composition I.      Photoinitiator 2 was 2,2diethoxyacetophenone.                                 DIPAE was 2(diisopropylamino)ethanol.                                         TOA was trioctylamine.                                                   

EXAMPLE 8

Compositions were prepared in which several differentpolydiorganosiloxanes and mercaptofunctional crosslinkers were used.These compositions produced high refractive index coatings withvalues >1.48. The compositions were made by blending the ingredients andwere as follows:

Composition IV

(a) 96.1 parts of a dimethylvinylsiloxy endblocked polydiorganosiloxanehaving 30 mole percent diphenylsiloxane units and 70 mole percentdimethylsiloxane units and having a degree of polymerization of 100.

(b) 2.0 parts of a mercaptofunctional crosslinker of the average formula##STR21## and

(c) 1.9 parts of a photoinitiator of the formula ##STR22##

Composition V

(a) 96.1 parts of a dimethylvinylsiloxy endblocked polydiorganosiloxanehaving 21 mole percent diphenylsiloxane units and 79 mole percentdimethylsiloxane units and having a degree of polymerization of 100.

(b) 2 parts of a mercaptofunctional crosslinker of the average formula##STR23## and

(c) 2 parts of the photoinitiator described in (c) of Composition IV.

Composition VI

96.1 parts of the dimethylvinylsiloxy endblocked polydiorganosiloxanedescribed in (a) of Composition V,

(b) 2.0 parts of the mercaptofunctional crosslinker as described in (b)of Composition V, and

(c) 4 parts of the photoinitiator as described in (c) of Composition IV.

Composition VII

(a) 96.1 parts of a dimethylvinylsiloxy endblocked polydiorganosiloxanehaving 21 mole percent diphenylsiloxane units and 79 mole percentdimethylsiloxane units and having a degree of polymerization of 200.

(b) 2 parts by weight of the mercaptofunctional crosslinker as describedin (b) of Composition VI.

(c) 2 parts of the photoinitiator as described in (c) of Composition IV,and

(d) 50 ppm of paramethoxyphenol as a storage stabilizer.

Composition VIII

(a) 96.1 parts of the dimethylvinylsiloxy endblockedpolydiorganosiloxane as described in (a) of Composition VII,

(b) 2 parts of a mercaptofunctional crosslinker of the average formula##STR24## and

(c) 2 parts of the photoinitiator as described in (c) of Composition IV.

Composition IX

(a) 96.1 parts of the dimethylvinylsiloxy endblockedpolydiorganosiloxane as described in (a) of Composition VII,

(b) 2 parts of the mercaptofunctional crosslinker as described in (b) ofComposition VIII,

(c) 2 parts of the photoinitiator as described in (c) of Composition VI,and

(d) 50 ppm of paramethoxyphenol as a storage stabilizer.

Composition X

(a) 96.1 parts of a dimethylvinylsiloxy endblocked polydiorganosiloxanehaving 21 mole percent diphenylsiloxane units and 79 mole percentdimethylsiloxane units and having a degree of polymerization of 300,

(b) 2 parts of the mercaptofunctional crosslinker as described in (b) ofComposition V, and

(c) 2 parts of the photoinitiator as described in (c) of Composition IV.

The above compositions were clear and were exposed to UV radiation withthe amount of energy received shown in Table VI. The 50% modulus, thetensile strength at break and the elongation at break were measured withthe results shown in Table VI.

                  TABLE VI                                                        ______________________________________                                                UV EX-    50%                ELONGA-                                  COMPO-  POSURE    MODULUS    TENSILE TION                                     SITION  mJ/cm.sup.2                                                                             kPa        kPa     %                                        ______________________________________                                        IV      224        96.5      206.8   150                                      V       224       213.7      275.8    80                                      VI      224       193.1      344.7   110                                      VII     224       137.9      310.3   180                                      VIII    224       158.6      310.3   145                                      IX      224       158.6      344.7   165                                      IX       24       131.0      379.2   220                                      X       224       --         172.4   150                                      ______________________________________                                    

The Composition IX cured with 24 mJ/cm² of UV radiation cured in 0.3seconds. This example showed that the compositions of this inventioncured in a very short time with low amounts of UV energy. The othercompositions would also cure in a short time, such as less than onesecond. Composition IX had a shelf life of greater than three months, aviscosity at 25° C. of 2.2 Pa's. and a refractive index of 1.488.

EXAMPLE 9

The use of mixtures of alkenyl containing polydiorganosiloxanes toprovide reinforcement to the cured elastomers is illustrated by thisexample.

Compositions were prepared by blending the ingredients as describedbelow to make homogeneous compatible materials:

Composition XI

(a) 137.5 parts of a dimethylvinylsiloxy endblocked polydimethylsiloxanehaving a degree of polymerization of about 300,

(b) 12.5 parts of a dimethylvinylsiloxy endblocked polydisiloxane having22.2 mole percent methylvinylsiloxane units and 77.8 mole percentdimethylsiloxane units and having a degree of polymerization of about450,

(c) 37.4 parts of Crosslinker I as described in Example 1, and

(d) 3.7 parts of the photoinitiator as described in (c) of CompositionIV.

Composition XII

(a) 137.5 parts of a dimethylvinylsiloxy endblocked polydimethylsiloxanehaving a degree of polymerization of about 300,

(b) 12.5 parts of a dimethylvinylsiloxy endblocked polydisiloxane having22.2 mole percent methylvinylsiloxane units and 77.8 mole percentdimethylsiloxane units and having a degree of polymerization of about450,

(c) 37.4 parts of Crosslinker I as described in Example 1,

(d) 3.7 parts of the photoinitiator as described in (c) of CompositionIV, and

(e) 3.7 parts of diisopropylaminoethanol as a storage stabilizer.

Composition XIII

(a) 100 parts of a dimethylvinylsiloxy endblocked polydiorganosiloxanehaving 25 mole percent diphenylsiloxane units and 75 mole percentdimethylsiloxane units and having a degree of polymerization of about200,

(b) 10 parts of a dimethylvinylsiloxy endblocked polydiorganosiloxanehaving 25 mole percent diphenylsiloxane units, 21 mole percentmethylvinylsiloxane units, and 54 mole percent dimethylsiloxane units,and having a degree of polymerization of about 300,

(c) an amount of the Crosslinker as described in Composition VIII ofExample 8 to provide a ratio of vinyl radical to mercapto group of1.00/1.00, and

(d) 2 weight percent of the photoinitiator as described in (c) ofComposition IV.

Composition XIV

(a) 100 parts of a dimethylvinylsiloxy endblocked polydiorganosiloxanehaving 25 mole percent diphenylsiloxane units and 75 mole percentdimethylsiloxane units and having a degree of polymerization of about200,

(b) 15 parts of a dimethylvinylsiloxy endblocked polydiorganosiloxanehaving 25 mole percent diphenylsiloxane units, 21 mole percentmethylvinylsiloxane units, and 54 mole percent dimethylsiloxane units,and having a degree of polymerization of about 300,

(c) an amount of the Crosslinker as described in Composition VIII ofExample 8 to provide a ratio of vinyl radical to mercapto group of1.00/1.00, and

(d) 2 weight percent of the photoinitiator as described in (c) ofComposition IV.

These compositions were cured by exposure to UV radiation in the amountof energy as described in Table VII. The tensile strength at break, theelongation at break, and the 50% modulus were measured on the curedelastomer and the results observed were as shown in Table VII.

                  TABLE VII                                                       ______________________________________                                                UV                  ELONGA-                                           COMPO-  ENERGY    TENSILE   TION    MODULUS                                   SITION  mJ/cm.sup.2                                                                             kPa       %       kPa                                       ______________________________________                                        XI      24        2137      240     193.1                                     XI      50        2068      290     158.6                                     XII     24        1034      170     151.7                                     XII     50        2551      245     186.2                                     XIII    10        1000      150     206.8                                     XIII    24        1172      160     262.0                                     XIII    50        1517      155     262.0                                     XIII    224       2344      175     268.9                                     XIV     15        1207      105     379.2                                     XIV     30        2068      120     393.0                                     XIV     60        1931      120     372.3                                     XIV     224       2034      120     400.0                                     ______________________________________                                    

EXAMPLE 10

This example shows reinforcing the compositions of this invention byusing resins. The compositions were prepared by blending the followingingredients to make the compositions which cure by exposure to UVradiation.

Composition XV

(a) 100 parts of the dimethylvinylsiloxy endblocked polydiorganosiloxaneas described in (a) of Composition XIV,

(b) 30 parts of a siloxane resin having 70 mole percentmonophenylsilsesquioxane units, 10 mole percent dimethylvinylsiloxyunits, and 20 mole percent trimethylsiloxy units,

(c) an amount of the Crosslinker as described in (c) of Composition VIIIof Example 8 to provide a ratio of vinyl radical to mercapto group of0.80/1.00, and

(d) 2 weight percent of the photoinitiator as described in (c) ofComposition IV.

Composition XVI

(a) 92.6 parts of dimethylvinylsiloxy endblockedpolymethylphenylsiloxane having a degree of polymerization of about 50,

(b) 45 parts of a siloxane resin having 70 mole percentmonophenylsilsesquioxane units and 30 mole percentmonopropylsilsesquioxane units and being endcapped withdimethylvinylsiloxy units and having a theoretical equivalent weight ofabout 1500 based on vinyl radical,

(c) 7.4 parts of trimethylolpropanetrimercaptoproprionate. and

(d) 2.9 parts of the photoinitiator as described in (c) of CompositionIV.

Composition XVII

(a) 93.9 parts of the dimethylvinylsiloxy endblockedpolymethylphenylsiloxane having a degree of polymerization of about 50,

(b) 45 parts of a siloxane resin as described in (b) of Composition XVIexcept the theoretical equivalent weight is about 3000 based on vinylradical.

(c) 6.1 parts of trimethylolpropanetrimercaptoproprionate, and

(d) 2.9 parts of the photoinitiator as described in (c) of CompositionIV.

Composition XVIII

(a) 91.8 parts of the dimethylvinylsiloxy endblockedpolymethylphenylsiloxane having a degree of polymerization of about 50,

(b) 45 parts of a siloxane resin having 75 mole percentmonophenylsilsesquioxane units, 7.9 mole dimethylvinylsiloxy units, and17.1 mole percent trimethylsiloxy units,

(c) 8.2 parts of trimethylolpropanetrimercaptoproprionate, and

(d) 2.9 parts of the photoinitiator as described in (c) of CompositionIV.

Composition XIX

(a) 91.8 parts of the dimethylvinylsiloxy endblockedpolymethylphenylsiloxane having a degree of polymerization of about 50,

(b) 45 parts of a siloxane resin having 85 mole percentmonophenylsilsesquioxane units 8.2 mole dimethylvinylsiloxy units, and6.8 mole percent trimethylsiloxy units,

(c) 8.2 parts of trimethylolpropanetrimercaptoproprionate, and

(d) 2.9 parts of the photoinitiator as described in (c) of CompositionIV.

Each of the above compositions were exposed to UV radiation in theamounts of energy stated in Table VIII. After the compositions werecured, the tensile strength at break, the elongation at break, and the50% modulus was measured and the values observed were as shown in TableVIII.

                  TABLE VIII                                                      ______________________________________                                                UV                  ELONGA-                                           COMPO-  ENERGY    TENSILE   TION    MODULUS                                   SITION  mJ/cm.sup.2                                                                             kPa       %       kPa                                       ______________________________________                                        XV      10        483       170     134.4                                     XV      24        621       175     158.6                                     XV      50        827       200     165.5                                     XV      224       655       160     167.5                                     XVI     50        552       120     234.4                                     XVI     225       517       115     220.6                                     XVII    50        448       245     117.2                                     XVII    225       483       205     151.7                                     XVIII   50        517       180     165.5                                     XVIII   225       655       200     179.3                                     XIX     50        793       230     179.3                                     XIX     225       827       205     220.6                                     ______________________________________                                    

That which is claimed is:
 1. An article comprising a substrate having atleast a surface of a composition in the cured state in which thecomposition comprises a material which is storable in one package, isviscosity stable indicated by the failure of the 25° C. viscosity todouble when heated at 100° C. for 24 hours, cured when exposed toultraviolet radiation of 70 millijoules or less per square centimeter inone second or less where the ultraviolet radiation includes a wavelengthof 365 nanometers, and is obtained by mixing(A) a mixture of at leastone polydiorganosiloxane having a low alkenyl radical content and atleast one polydiorganosiloxane having a high alkenyl radical contentwherein the polydiorganosiloxanes are alkenyl functional, lineartriorganosiloxy endblocked polydiorganosiloxane having a degree ofpolymerization of 30 to 1,000 where each silicon-bonded organic radicalis selected from the group consisting of vinyl, methyl, phenyl,3,3,3-trifluoropropyl, beta-(cyclohexenyl)ethyl, ethyl, cyclohexenyl,allyl, high alkenyl radicals represented by the formula --R*(CH₂)_(r)CH═CH₂ where R* is ═(CH₂)_(s) -- or --(ch₂)_(t) CH═CH, r has a value of1, 2, or 3; s has a value of 3 or 6; and t has a value or 3, 4, or 5,and silacyclopentenyl, and having per molecule at least twosilicon-bonded organic radicals selected from the group consisting ofvinyl, beta-(cyclohexenyl)ethyl, cyclohexenyl, allyl, higher alkenylradical, and silacyclopentenyl, (B) mercapto functional crosslinkerwhich is at least one material selected from the group consisting ofmercapto functional polyorganosiloxanes and mercapto organic compounds,said mercapto functional polyorganosiloxanes are represented by thegeneral formula

    R"R'.sub.2 SiO(R"'R'SiO).sub.x (R'RSiO).sub.y SiR'.sub.2 R"

wherein each R is a mercaptoalkyl radical having from 2 to 6 carbonatoms per radical; each R' is selected from the group consisting ofmethyl, phenyl, 3,3,3-trifluoropropyl, and ethy; and each R" is aradical selected from the group consisting of --OH, R, and R'; and eachR"'is methyl or phenyl, on the average there being per molecule at leasttwo mercaptoalkyl radicals, x is 0 or great, y is 0 or greater, and theamount and kind of organic radicals represented by R, R', R", or R"'being of such a nature as to make (A) and (B) compatible, and saidmercapto organic compounds have at least two mercapto groups permolecule, consisting of atoms of sulfur, carbon, and hydrogen, andoptionally oxygen, having a molecular weight less then 1,000 and beingof such a nature as to make (A) and (B) compatible, (C) photosensitizer,and (D) storage stabilizerthere being in said material from 0.5 to 1.5total alkenyl radicals per mercapto group.
 2. The article according toclaim 1 in which the substrate is glass.
 3. The article according toclaim 2 in which the glass is an optical fiber.
 4. The article accordingto claim 3 in which the cured composition is a primary coat.